Quantification of the material inhomogeneity effect in thin metallic film stacks

Darjan Kozic

Research output: ThesisDoctoral Thesis

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Abstract

This thesis deals with the characterization of thin metallic film systems with respect to their mechanical properties. This incorporates investigations about the intrinsic properties, internal loading conditions and the response to external mechanical loading of the material systems. Compressive and tensile residual stresses in thin films have implications on the reliability of microelectronic components. Residual stresses can have a negative or a positive effect on the performance and lifetime of the structures. In this thesis, a method is developed to efficiently determine residual stresses in thin films. This is realized by combining micro-mechanical experiments and computational methods. Experimental results, obtained with the so-called Ion beam Layer Removal method, are utilized to inversely determine the residual stresses numerically with finite element simulations or analytically with the Euler-Bernoulli beam theory. It is shown that the residual stresses in various thin film systems can be locally resolved with high precision. The material behavior of thin films is determined by their size and the internal structure. The nanocrystalline nature of the investigated materials allows for a classical approach to derive the yield and hardening behavior. The force-displacement response from spherical nanoindentation experiments is used in an optimization routine – coupled to finite element analysis – to numerically determine the flow curve of the thin films while also considering the residual stresses. It is shown that the flow behavior of miniaturized materials is different compared to macroscopic or bulk materials. To describe the fracture behavior of the thin film stacks under external loading, the concept of configurational forces is applied. The investigation is especially focused on the influence of the residual stress state and material properties on the crack driving force. A crack can experience shielding or anti-shielding in the vicinity of an interface. This impact on the crack driving force is described by the interface inhomogeneity term. Another contribution to the term is given by the jump of the residual stress at the interfaces. In addition, the residual stress gradient in the layers further influences the crack driving force. This contribution to the crack driving force is given by the gradient inhomogeneity term. The mechanical behavior of thin film components has an integral significance for the performance and life span of high-end microelectronic devices. This thesis offers tools for thin film stack characterization which can be readily applied in the design chain of components.
Translated title of the contributionQuantifizierung vom Effekt der Materialinhomogenitäten in dünnen metallischen Schichtsystemen
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Kiener, Daniel, Assessor B (internal)
  • Antretter, Thomas, Assessor A (internal)
Publication statusPublished - 2017

Bibliographical note

embargoed until null

Keywords

  • Mechanical Properties
  • Residual Stresses
  • Material Behavior
  • Crack Driving Force
  • Finite Elements
  • Configurational Force Concept

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